The present invention relates generally to ion implantation systems, and more particularly, to heating assemblies for raising the temperature of a wafer to an elevated level within an evacuated chamber of an ion implantation system.
Processing of semiconductor wafers by ion implantation is routinely practiced in manufacturing integrated circuits. Ion implantation is typically performed in an evacuated chamber in which a semiconductor wafer is exposed to a beam of ions having a selected energy. In some ion implantation techniques, the wafer is heated to elevated temperatures during ion implantation steps to dynamically anneal defects generated in the wafer as a result of ion bombardment, and/or during subsequent annealing steps.
Heating a substrate within the vacuum environment of an ion implantation chamber has proven difficult. Many materials, especially heating lamps, fail quickly when heated in a vacuum environment, especially if provisions for cooling the lamps are not provided. Typically, metal blocks are utilized to mount the lamps in order to provide a heat sink for dissipating the heat generated by the lamps. It has generally been thought that a metal, such as copper, with very high thermal conductivity is the ideal choice for such a mounting block. Copper is also preferred because it is easy to electroplate, thereby facilitating the deposition of mirror-like reflective coatings. By coating the surface of the block that lies behind the lamp, the efficiency of radiant heat transfer is enhanced.
Nonetheless, copper mounting blocks have a number of drawbacks, not the least of which is that copper is difficult to machine. Internal networks for transmitting cooling fluids within the block need to be bored or otherwise machined into the block, but due to the relative softness of copper and copper alloys, the conventional copper mounting block is usually constructed from multiple pieces, each machined with a portion of the required networks. The pieces must then braised together and tested for integrity. Multiple-piece braised components subjected to large-gradient temperatures can be prone to leakage and other structural failures, as well as requiring complex and time-consuming manufacturing and assembly techniques.
Accordingly, there is a need for simpler heating devices that can withstand the rigors of a vacuum environment and repeated heating with greater ease of manufacturing. There is also a need for such heating devices that can perform in a vacuum environment without failure over extended time periods.
The present invention provides a heating assembly that includes a thermally conductive, lamp-mounting block manufactured from aluminum or a similar material, which can be machined as a single-piece (e.g., unibody) block. The unibody block includes one or more networks of inner passageways bored or otherwise machined within the block for transporting one or more cooling fluids. The mounting block can also have a reflective coating on one or more of its surfaces that face the lamps to efficiently reflect heat and/or light generated by the lamps onto a desired surface, for example, a semiconductor wafer. Thermal isolation devices, e.g., pads, provide for both physical mounting of the heating lamps to the mounting block and also provide thermal isolation between the heating lamp and its electrical connections are also disclosed for protecting heat-sensitive elements of the heating assembly such as seals.
In one aspect, the thermally conductive block can include a plurality of openings formed therein that are in fluid communication with at least one of the inner passageways. The openings are preferably formed in proximity of the lamps to allow a flow of a cooling fluid circulating through the passageways onto the lamps, thereby cooling the lamps. The openings can be formed along the length of a heating lamp, for example, in a single row, or in multiple rows each positioned at one side of the lamp. In some embodiments, two rows of openings are utilized in which the openings in one row are offset relative to those in the other row to maximize the area of the lamp that will be in contact with the cooling fluid. Those having ordinary skill in the art will appreciate that other arrangements of openings can also be utilized so long as the flow of a cooling fluid through the openings is substantially directed onto a lamp to be cooled.
In a related aspect, the passageway that is in fluid communication with the openings can receive a gaseous cooling fluid (e.g., air or nitrogen) and allow it to expand on and around the heating lamp, via the plurality of openings, to remove heat generated by the lamps. Another passageway can be utilized to circulate a cooling fluid, e.g., water, through the block from an inlet port to an outlet port.
In further aspects, the heating assembly can include a cover, for example, a quartz tube, in which the lamp and block can be disposed. One or more seals, for example, O-ring seals, formed in the block can seal the cover, thereby insulating the lamps from an external environment in which the heating assembly is positioned.
In another aspect, the thermally conductive block is formed of aluminum, and is coated with a highly reflective material, such as, gold. A primer layer, for example, a nickel layer, can be applied to the aluminum block prior to application of the high reflective coating in order to enhance the adhesion of the reflective coating to the block. The use of aluminum for forming the block is particularly advantageous in that it allows readily forming the inner passageways in the block.
Still another aspect of the invention, the thermally conductive block is manufactured as a unibody construction. Internal networks of passageways can be manufactured via xe2x80x9cgun-drillingxe2x80x9d methods and techniques, for example.
The present invention also provides a heating assembly for use in an ion implantation system that includes a heating assembly formed of a lamp and a thermally conductive block holding the lamp. The lamp is capable of heating a silicon wafer during the implantation process for reducing or eliminating surface damage, particularly amorphous layering, of the wafer. The thermally conductive block has a layer of gold over a primer layer to increase efficiency and reduce parasitic heating of the block. Further, the block has a series of passageways through which a cooling fluid can be circulated to remove heat, as well as a series of passageways through which a compressible cooling fluid can be introduced and expanded over and around the lamp. The assembly is surrounded by a cover, e.g., a quartz tube, sealed at each end providing separation of the heating assembly environment from the vacuum of the ion implantation device. The invention also includes a mount supplying a physical attachment for the heating assembly, and also couplings for electrical supplies and cooling fluid inlets and outlets.
A heating assembly according to the invention can be utilized in a variety of different applications. For example, such a heating assembly can be employed in an evacuated chamber of an ion implantation chamber to provide heating of semiconductor wafers during ion implantation and/or annealing steps. In such an application, the heating assembly can be coupled to a mount for stable positioning within an end station of the ion implantation chamber. The mount can include inlet and outlet ports to allow flow of cooling fluids from an external source into the inner passageways of the block.
Further understanding of the invention can be obtained by reference to the following detailed description in conjunction with associated drawings which are briefly described below.